1) Field of the Invention
The present invention relates to a disk array apparatus, and more particularly to a system power supply and a backup power supply in the disk array apparatus.
2) Description of the Related Art
In recent years, various kinds of data are treated on computers in an electronic form and an amount of the data is in an increasing trend. Therefore, a storage that efficiently stores a large amount of data is demanded. A disk array apparatus is one example of such storage.
The disk array apparatus applies a technology of a redundant array of inexpensive disks (RAID). In the RAID, more than one hard disk is connected in parallel, and the hard disks connected are managed as a single unit of a hard disk.
The RAID includes a RAID-0 in which identical data is stored in each of several hard disks and RAID-5 in which data is stored while distributing parity information of the data to hard disks. Use of the RAID realizes improved reliability of data to be stored.
Generally, a disk array apparatus includes a cache memory to reduce a time required for accessing data that is stored in the disk array apparatus. The cache memory also applies a measure for improving reliability of the data. For example, a block check character (BCC) is written in several hard disks for protecting the data, or the same data is stored in two cache memories for mirroring.
For the improved reliability of the data, a measure to improve physical and electrical reliability of the data is also required in addition to such a logical data protection described above. Such measure includes protection of data at the time of power failure. The disk array apparatus operates with power that is supplied from an external power supply, such as a commercial power supply. Therefore, in case of power failure, data that is being processed can be lost. To prevent loss of the data, the disk array apparatus includes a backup power supply.
Specifically, when the disk array apparatus detects power failure, a controller of the disk array apparatus suspends operation under processing. Then, the controller notifies a host computer of occurrence of the power failure and executes a backup processing. In the backup processing, data that is held in a volatile cache memory, which is data that can be lost due to the power failure, in a hard disk. A time required for the backup processing ranges from several minutes to several tens of minutes depending on a capacity of the cache memory and the number of hard disks in which the data in the cache memory is to be written. Since power is not supplied from the external power supply during the backup processing, the disk array apparatus includes the backup power supply that supplies power for executing the backup processing.
Conventionally, various technologies relating to the backup power supply have been proposed. For example, Japanese Patent Application Laid-Open No. 2000-184615 discloses a technology for managing a battery, which is the backup power supply, to prevent deterioration of the battery.
Specifically, in the above conventional technology, the battery includes a battery management device with which charging control considering a remaining amount of power in the battery is carried out. In addition, a battery pack itself interrupts a charging current. Thus, the battery is prevented from being overcharged, thereby retarding deterioration of the battery. Furthermore, during standby for backup, the battery is charged when the remaining amount of power decreases to a specified amount, thereby resolving insufficiency of power during the standby for backup.
When the disk array apparatus detects power failure, the disk array apparatus switches a power supply from a power supply unit, which generates a voltage used in the disk array apparatus from power supplied from an external power supply, to a battery unit for backup in the disk array apparatus. Specifically, when the disk array apparatus detects power failure, the power supply unit outputs a power-failure detection notice to a monitoring unit that performs switching control for switching a power supplying unit. The monitoring unit outputs a power-failure processing notice to a controller that causes a hard disk to execute the backup processing, and outputs, to the battery unit, an instruction to start supply of power. When the battery unit receives the instruction, the battery unit starts discharge to supply a voltage to a power supply line in the disk array apparatus.
However, a certain amount of time is required for the battery unit to be able to stably supply a voltage of an actually required level after reception the instruction. In other words, that there is a period in which a predetermined voltage is not supplied to the power supply line until the battery unit stably supplies the voltage of the actually required level after detection of the power failure.
To solve such a problem, it is necessary to provide a power supply unit that can supply a voltage to the power supply line during the time (battery warm-up time) until the battery unit supplies the voltage of the required level to the power supply line after detection of the power failure. Therefore, a large capacity capacitor is required to provide a time in which an output is maintained such that the predetermined voltage is supplied to the power supply line even if power is cut from the external power supply. As a result, a size of a circuit of the power supply unit increases.
In addition, the battery warm-up time that is different depending on specifications required for each disk array apparatus requires a custom power supply unit for each disk array apparatus. As a result, a manufacturing cost of the disk array apparatus increases.